CREATE FUNCTION

create_function ::= CREATE [ OR REPLACE ] FUNCTION function_name 
                    ( [ parameter_list ] )
                    RETURNS return_type
                    LANGUAGE language_name
                    [ SECURITY { DEFINER | INVOKER } ]
                    [ volatility ]
                    [ STRICT ]
                    AS function_body

function_name ::= [schema.]name

parameter_list ::= parameter [, ...]

parameter ::= [ parameter_mode ] [ parameter_name ] parameter_type [ DEFAULT default_value ]

parameter_mode ::= IN | OUT | INOUT

argument_list ::= data_type [, ...]

return_type ::= data_type
              | SETOF data_type
              | TABLE ( column_name data_type [, ...] )
              | trigger

language_name ::= plpgsql | sql | c | internal

volatility ::= IMMUTABLE | STABLE | VOLATILE

function_body ::= 'definition'
                | $$definition$$
                | $tag$definition$tag$

CREATE OR REPLACE FUNCTION [schema.]function_name(
    parameter_name parameter_type[ DEFAULT default_value][,
    ...]
)
RETURNS return_type
LANGUAGE language_name
SECURITY { DEFINER | INVOKER }
[ IMMUTABLE | STABLE | VOLATILE ]
[ STRICT ]
AS $tag$function_body$tag$;